The reuptake system for dopamine includes at least three functional components: a specific carrier system with dopamine recognition sites, a regulatory site characterized by high-affinity recognition sites for uptake inhibitors and a coupling device that links together the regulatory and carrier sites. Sodium-dependent 3H-cocaine binding sites are located exclusively on dopaminergic terminals in caudate nucleus. An endogenous polypeptide present in synaptosomes displaces 3H-cocaine from its binding sites in a non-competitive fashion and inhibits dopamine uptake. Its apparent molecular weight is 17,500 and its amino acid composition shows the presence of high amounts of basic amino acid residues. It is postulated that the cocaine recognition sites may be associated with the dopamine carrier through this basic regulator protein.